1. Field of the Invention
The present invention relates to a communication system, a communication apparatus, a display apparatus, and a communication method.
2. Description of the Related Art
According to a WUSB (Wireless Universal Serial Bus) 1.0 specification, in data communication between a host and a device, use of an encryption based on a secret key is defined. Two types of secret key exchange methods employed in the WUSB 1.0 specification is defined in the WUSB Association 1.0 specification.
One method is an exchange of a secret key based on a public key cryptosystem through a wireless communication and the other method is an exchange of a secret key through a wired communication. The former method is referred to as Numeric Model, as numerals are derived for confirming the integrity of the secret key during a secret key derivation. The latter method is referred to as Cable Model, as a cable is used for realizing a USB 2.0 host-device communication by using a USB (Universal Serial Bus) 2.0 specification. According to the WUSB Association 1.0 specification, the WUSB host must have implementation of both the methods and the WUSB device must have at least one of the above-described methods.
The Numeric Model provides for an improvement in usability as it is possible to exchange the secret key through the wireless communication. However, it is necessary to provide a display apparatus for displaying the numerals. The Cable Model is based on reliable secret key exchange, as the communication is performed by using a cable with a USB 2.0 host/device controller but the controller and the connector need to be implemented.
The WUSB 1.0 specification defines a DWA (Device Wire Adapter) and also the WUSB Association 1.0 specification is applied to the DWA.
The DWA must use one of two Association Models. However, when the Numeric Model is used, a display apparatus needs to be implemented in the DWA and the display apparatus increases the costs. Also, implementation of the display apparatus complicates the configuration and it is difficult to achieve miniaturization.
When the Cable Model is used, the secret key exchange method becomes simple and reliable. On the other hand, the USB 2.0 device controller for a connection to the WUSB host and a connector for an external connection increase the costs.